Semiconductor devices having metal oxide layers of adjacent epitaxial p-type and n-type structures that form p-n junctions are known as semiconductor diodes, or p-n diodes. Such devices are useful as light emitting diodes (LEDs) and power transistors. The further development of this technology has enabled semiconductor diode efficiency to rise exponentially, making them more widely useful in various applications. Among recent research trends are those that seek to reduce costs of producing semiconductor diodes, while enlarging the diode surface area and maintaining high performance and efficiency.
Generally, semiconductor diodes are manufactured using single crystal substrates of GaN, ZnO, Al2O3 (sapphire), SiC, SiO2 (quartz) and silicon. Large area substrates (e.g., greater than about 15.24 centimeters (cm) (6 inches)) of single crystal GaN and ZnO are not widely used due to their high cost, even though their lattice matching with p-type and n-type films is almost equal, which permits growth of superior quality single crystalline epitaxial films for making the best LEDs.
Silicon is known to be among the least costly of the suitable semiconductor substrate materials, with high quality single crystal wafers having large surface area with about 20.32 cm (8 inches) to about 30.48 cm (12 inches) in diameter, or greater, available for deposition of metal oxide layers thereon. However, silicon substrates have their own drawbacks, including large lattice mismatch and increased warping as their surface area increases. This hinders growth of high quality epitaxial layers of GaN, ZnO, or other oxides thereon and subjects the deposited epitaxial layers to stress that increases the risk of defects or other distortion of the crystal structures.
Many techniques have been developed to reduce the lattice mismatch, such as first depositing MgO thin layers on the Si-based substrate, then growing an AlGaN layer, and finally depositing GaN p- and n-type epitaxial layers. Still, there remain unacceptable degrees of defects in the quality of the epitaxial layers, which reduce the efficiency of semiconductor diodes produced this way.
Additionally, after formation of the p- and n-type epitaxial layers, the substrate and possibly one or more of the intermediate layers, sometimes referred to as sacrificial layers, may be separated from the p- and n-type epitaxial layers to produce a free standing semiconductor device and a “reusable substrate” that can be used again to form another semiconductor device. The free standing semiconductor device has a smaller thickness, which may be advantageous depending on how and where the semiconductor device will be used. Thus, layers that were beneficial while forming the p- and n-type epitaxial layers of the semiconductor device, but which are unnecessary for its ongoing operation, have been removed. Some methods of removing sacrificial layers will not damage the substrate and, therefore, enable reuse of the substrate to grow new semiconductor layers. However, the reusable substrate will still present the same challenge during reuse as it originally presented, that is, large lattice mismatch that hinders growth of high quality epitaxial layers thereon.
Accordingly, it is desirable to provide high quality reusable substrate bases that use less expensive Si-based substrates and that permit the growth of high quality epitaxial layers thereon, notwithstanding the lattice mismatch between Si and GaN. In addition, it is desirable to provide semiconductor devices that use such reusable substrates. It is also desirable to provide methods for preparing such high quality multilayer semiconductor devices which can be subjected to a separation procedure to produce reusable substrate bases having Si-based substrates and free standing semiconductor devices. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.